Fiber gratings are incorporated into components that form the backbone of modern information and communications technologies, and are suitable for a wide range of applications, such as information processing and optical fiber communication systems utilizing wavelength division multiplexing (WDM). There are many different fiber grating types and configurations, with a wide variety of capabilities. For example, fiber Bragg gratings are useful in lasing, filtering and sensing applications. Various Bragg grating configurations also include chirped fiber gratings useful in chromatic dispersion compensators and apodized fiber gratings that are used to eliminate sidelobes in signal transmission spectra. Another type of fiber grating—a long period grating—is of particular interest in sensing and filtering applications. Light passing through a long period grating is modified rather than reflected, as occurs in fiber Bragg gratings. Also, unlike a fiber Bragg grating, a long period grating is typically used for coupling the mode of the fiber core into the fiber cladding. A long period grating has a spectral characteristic with multiple transmission gaps. The positions of these gaps along the spectral range depend on the refractive index of a medium outside the cladding of the fiber. Thus, changing the outside refractive index produces a shift in the transmission gaps. Typically, the period of a long period grating is significantly longer than the wavelength of light passing through the grating.
However, there are also a number of important applications for which an optical fiber grating constructed and configured to produce at least one spectral dip (corresponding to at least one predefined wavelength) in the transmission spectrum of a light signal being transmitted therethrough, for which such a grating would be the only practical solution, or for which it would be the best solution (or at least a more optimal solution than a long period grating). This is especially the case in applications where fiber gratings of very small lengths are desirable or necessary.
There are also useful applications for which it would be advantageous to provide the above-described diffraction grating that is substantially produced from a single material (as opposed to conventional gratings which typically have cores and claddings of different materials (or which may use the same material for the core and cladding with one of the materials being doped by another material), to ensure a predetermined minimum index contrast value therebetween. Additionally, there are applications for which it would be useful to have a grating capable of producing at least one spectral peak in its core light transmission spectrum, corresponding to at least one predetermined wavelength.
It would thus be desirable to provide an optical fiber grating for controlling the light signal transmission therethrough by diffracting a portion of the transmitted light signal at at least one predefined wavelength thereof, causing at least one of: at least one predetermined spectral dip, and/or at least one predetermined peak, in the resulting light transmission spectrum, each corresponding to the at least one wavelength of the diffracted portions(s) of the transmitted light signal. It would also be desirable to provide the above-described fiber optic diffraction grating that may be readily fabricated in its entirety from a single material.